This invention relates generally to the cleaning of glass sheets in apparatus wherein glass sheets are successively transported by a conveyor system through washing and drying zones, and it more particularly pertains to such apparatus particularly designed for cleaning bent or curved sheets or plates of glass.
It is common industrial practice to clean substantially large sheets of glass by providing equipment including a conveyor system that continuously moves successive glass sheets first through an enclosed tunnel-like washing and rinsing zone and then through a drying zone. The degree of required cleanliness determines the complexity of the equipment utilized in the washing and rinsing operation. A relatively simple water flushing and brushing process may be used where the glass sheets need only be generally visibly clean. Absence of finger marks, streaks, or spots on the sheets may require more intensive brushing and use of a heated detergent solution prior to rinsing. Greater degrees of cleanliness may be required where the glass sheets are intended for insulating, laminating, silvering, or vacuum coating processes, and for such needs, chemical-free or even clinical cleanliness can be accomplished by the provision of specialized brushing equipment, repetition of steps in the washing process, and more thorough or repeated rinsing.
It is typical, following the washing and rinsing steps, to convey the glass sheets through a drying zone where rinse water is removed such that the sheets are dispensed from the conveyor in a perfectly dry condition for packing or a subsequent manufacturing operation. In some relatively low-efficiency glass water=dryer equipment, the glass sheets are dried by application of heated rinse water which is allowed to evaporate from the glass surface. This method typically results in water spotting and does not accomplish effective drying of the glass edges. More advanced systems virtually eliminate water spotting by accomplishing the drying operation through the use of a high-pressure air stream applied to the glass sheet surfaces. Each glass sheet, supported by the conveyor, is moved past an adjacent slot elongated to reach across the entire sheet, and the high-intensity blower-driven air stream is emitted close to the sheet surface at a predetermined angle to peel the water and any other impurities from the glass surface and blow them rearwardly as the glass sheet progresses forwardly on the conveyor. The structure which distributes the air stream against the glass, including the aforementioned slot, is referred to in the industry as an air knife. A plurality of spaced-apart air knives may be utilized whereby the glass sheet, as it progresses on the conveyor, may be subjected to successive high-intensity air stream applications to effect thorough drying of the sheet.
The typical air knife assembly includes an elongated box-like enclosed chamber or plenum disposed to extend transverse to the pathway of the conveyor on which the successive glass sheets are supported. From a remote stationary heavy-duty blower, a continuous air flow is conducted into the plenum through an interconnecting conduit, and the air flow is distributed from the plenum through a longitudinal slot as a high velocity curtain-like air stream striking the glass surface on a line extending entirely across the sheet.
For the cleaning of curved glass sheets which present one concave surface and an opposite convex surface, it is common practice to provide a conveyor system adapted to support the sheets from beneath, for travel in a horizontal pathway, with the sheets oriented with the axis of their curvature parallel to the pathway. For such specialized cleaning equipment, air knives have been developed where the structure defining the air stream distribution slot has a rigid sweeping curvature so that the slot is positioned closely parallel to the curved glass sheet surface conveyed past the slot during the drying operation. Such equipment has proven very effective for its desired purpose but is limited in its application to the cleaning only of curved glass sheets to which the air knives are shaped to conform. Such machinery has been adapted to permit conversion by substitution of appropriately shaped air knives consistent with the particular curvature of glass sheets to be subjected to a cleaning operation. Such conversion, however, necessitates the special construction of differently shaped air knives, each shape suitable only for drying glass sheets of a particular curvature. This involves high manufacturing costs and the additional operating expenses associated with extensive conversion down time.